Semiconductor wafers are subjected to numerous steps during processing in various pieces of processing equipment. The wafers must be transported from workstation to workstation and often must be temporarily stored in order to accommodate the necessary processing steps. Usually such transport and storage is accomplished by putting the wafers into sealed containers to minimize exposure of the wafers to environmental contaminants.
Numerous configurations of carriers have been previously known for handling, storing, and shipping wafers. A common component in carriers configured as closable containers is a molded plastic member known as a cushion to stabilize the positioning of wafers in the container. Such shipping containers with cushions have been previously known as disclosed, for example, in U.S. Pat. Nos. 4,043,451; 4,248,346; 4,555,024; 5,253,755; 5,273,159 and 5,586,658. These types of containers typically include vertical wafer-receiving channels and cushions at the upper and/or lower ends.
These shipping devices have typically been designed to transport wafers or disks in a vertical orientation from place to place, whereas most processing workstations require that wafer processing carriers retain wafers horizontally. Thus, wafers must be reoriented for many processing steps. Where the entire container is reoriented with wafers in place, the wafers can shift and scrape against the wafer pockets, producing particulates.
Corresponding with the increase in the size of wafers being processed into semiconductor chips, the industry is also shifting from vertically oriented containers to containers that maintain the wafers horizontally. Forward wafer restraints for such carriers have comprised a cushion member attached to the door and extending vertically and transverse to the planes of the wafers to engage each wafer along a vertical line. The cushions may be fixed to the inside surface of the door such that they engage the stack of wafers as the door is inserted into the door frame; or, alternatively, the cushions may be attached to mechanisms in the door to extend and retract the cushions independently of the movement of the door into and out of the door frame. For a more detailed discussion, reference is made to U.S. Pat. No. 5,711,427, which is incorporated herein by reference.
With the vertically oriented carrier, wafer receiving channels are designed to hold wafers firmly with a minimum of horizontal movement. With the horizontally oriented carrier, wafer receiving slots are larger than the thickness of wafers to enable wafers to be inserted horizontally into containers and lowered onto a seating position on wafer shelves. To avoid particulate generation, there will ideally be no sliding of the wafer on the wafer shelves. In such carriers, now known as transport modules, contact with the wafers by the carrier is desirably kept to a minimum. Minimal contact with the wafers is believed to create minimal opportunity for particulate generation and particulate contamination of the wafers. In one example, U.S. Pat. No. 5,788,082, which is herein incorporated by reference, discloses shelves and integral beads that provide the minimal contact as being made from specialized abrasion-resistant materials.
Conventional individual resilient fingers for engaging wafers, whether for horizontal or vertically oriented wafers, have a configuration of a V-shape with a bottom wafer-seating portion that is sized to the thickness of the wafer to hold the same securely. Moreover, each wafer is supported at the same circumferential position. That is, the cushions are arranged in a linear row or column. The spacing between horizontal wafers in 300 mm front opening carriers has been standardized by the industry to allow maximum density in the carriers while still allowing insertion room for a robotic arm for insertion and removal. This minimal amount of vertical space makes it extremely difficult to manufacture cushions with vertically aligned wafer engaging fingers and wafer engaging portions that have any allowance for slight vertical misalignments in the wafer engaging portions, such as might be caused by variation in manufacture of the cushions or wafers misaligned on the shelves.
Accordingly, there is a need for a wafer cushion system that provides a forward constraint for sealable wafer enclosures, inhibits wafer movement while in the wafer carrier so as to prevent flutter, compensates for manufacturing variations and provides for wafer-cushion engagement portion misalignments.